π‐Stacked Donor–Acceptor Dendrimers for Highly Efficient White Electroluminescence

Abstract

p-Stacked dendrimers consisting of cofacially aligned donors and acceptors are developed by introducing three dendritic teracridan donors with orthogonal configuration and three triazine acceptors in periphery of hexaphenylbenzenes keleton. The dendritic structure and orthogonal configuration of teracridan not only make their outer acridan segments approaching to acceptor in close distance,but also fix donor and acceptor in face-to-face alignment, leading to through-space charge transfer emission with thermally activated delayed fluorescence (TADF) effect. By regulating charge transfer strength via substituent effect of acceptor, emission color of the dendrimers can be tuned from blue to yellow/red region. Solution-processed two-color white organic light-emitting diodes (OLEDs) based on blue and yellow pstacked donor-acceptor dendrimers exhibit the maximum external quantum efficiency of 20.6 %a nd maximum power efficiency of 58.9 lm W À1 ,r epresenting the state-of-the-art efficiency for all-TADF white OLEDs by solution process.

Acceptor-Donor-Acceptor π -Stacking Boosts Intramolecular Through-Space Charge Transfer towards Efficient Red TADF and High-Performance OLEDs

“…Variable temperature transient PL characteristic of DPXZ-2QX clearly confirms the TADF mechanism (Figure 4 (d)). To the best of our knowledge, all compounds except TPA-QX represent the rare examples of orange-red to red TSCT-TADF emitters in the literature [25,28]. Remarkably, the average delayed fluorescence lifetimes (τ d ) are reduced from 26.9 and 6.8 μs for DPXZ-QX and DPXZ-DFQX to 8.7 and 4.9 μs for DPXZ-2QX and DPXZ-2DFQX, respectively.…”

“…The maximum EQE/current efficiency/power efficiency are recorded as 23.2%/38.6 cd A -1 / 30.3 lm W -1 , respectively, for the device with 6 wt% DPXZ-2QX. The efficiencies are twofolds higher than the previous record value for red TSCT-TADF OLEDs (Figure 5(f)) [28]. It is worth mentioning that most of the red TBCT- TADF emitters in the literature use triphenylamine (TPA) and its substituted derivatives as the donor [42-49, 62, 63].…”

“…Alternatively, construction of molecular scaffolds featuring intramolecular through-space charge transfer (TSCT) excited states as opposed to through-bond charge transfer (TBCT) between the D and A offers another molecular design of TADF emitters on account of their intrinsically small ΔE ST values [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], whereas early efforts to develop TSCT-TADF molecules have been frustrated by the weak through-space electronic coupling within the D-A pair and the presence of abundant intramolecular motions [17][18][19][20][21]. In this context, significant enhancements in photo-and electroluminescence efficiencies have recently been achieved for TSCT-TADF small molecules, polymers, and dendrimers (Figure S1) [22][23][24][25][26][27][28][29][30][31][32][33]. Remarkably, Kaji and coworkers reported a significantly boosted RISC rate for a triptycene-supported molecule by virtue of a vibronically coupled spin-orbit coupling (SOC) effect [30].…”

“…The space-confining effect has been exploited for greatly suppressing the nonradiative decay of TSCT excited states [31][32][33]. However, high-efficiency TSCT-TADF emissions have been mainly limited to the blue-to-green regime with only few reports on relatively weak red emissions [25,28]. Although various D-A combinations have been developed for widely tuning the colours of TBCT-TADF emitters, they may not be well suited for the design of TSCT-TADF emitters if their geometric structures do not favour through-space interactions [34].…”

Exciplex polymer with strong AIE for constructing fully-solution-processed organic light-emitting diodes with 100-fold efficiency improvement compared to physically blended exciplex

“…[18][19][20] To further extend the material design idea and avoid the influence of D-A direct connection, exciplex materials with separated donors and acceptors have also been explored to achieve specific TADF through space charge transfer. [21][22][23][24] Because of the spatially separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), exciplex materials exhibit an intrinsic decreased exchange energy that simultaneously results in a small singlet-triplet energy gap (ΔE ST ), which is beneficial for reverse intersystem crossing (RISC) of triplet energy. [25][26][27][28][29] Moreover, an exciplex generally combines both electron-and hole-transporting components, which ensure a negligible carrier injection barrier, balanced charge transport, and an enlarged recombination zone.…”